The key features of percutaneous coronary intervention with chronic total obstruction lesion of right coronary artery

Abstract

We summarize recent research on percutaneous coronary intervention of chronic total occlusion of the right coronary artery. We then explain the method and technology of forward and backward revascularization in chronic total occlusion of the right coronary artery. Finally, we emphasize the monitoring methods and key treating measures for better prognosis of the patients.

Introduction

Percutaneous coronary intervention (PCI) is one of the key strategies in managing coronary artery disease (CAD) [Erdogan et al. 2013]. Chronic total occlusion (CTO) of the right coronary artery (RCA) is considered the most difficult of the three coronary artery diseases. Many studies have shown that the RCA revascularization ratio is the lowest [Claessen et al. 2013] and restenosis or blocking ratio of RCA bypass grafting (CABG) vessels in 3–5 years is >50% [Brady et al. 2013; Stiermaier et al. 2013]. Most doctors and patients would like to perform PCI because it can be done repeatedly, but it is difficult.

RCA anatomical features

The RCA originates from the right aortal root segment. The ‘C’ size of RCA descends down the surface of the right and left ventricals until it reaches the bottom of the heart. The beginning and the later segment of the RCA is often circuitous and has angulation, which makes PCI very difficult. Another problem is that the RCA originates lower down than the left coronary artery (LCA), which makes the holding power of the right-guiding catheter poor.

Pathological characteristics of RCA CTO lesion

Many studies have shown that CTO lesion can be classified as three types [Taniguchi et al. 2011]. The first has some mini passageway which allows the wire to pass through easily. The second type is where the CTO lesion is solid but not hard, and thus the wire can get through the lesion by normal technology. The third type is where it is too difficult to make the wire pass through the lesion.

Calcification of lesions exists in almost all CTO, lying in the intima and/or extima. The intimal calcification does not develop. Only the extimal calcification can develop some film. The main components of CTO lesions are fiber texture and scar tissue. A small portion of the remaining components are lipid pool and calcified tissue. The calcific degree can be classified as light, medium and substantial [Liu et al. 2011]. The last type requires the use of special stenting technology.

Imaging features of RCA CTO

RCA CTO has some imaging features. The first is a block on blood flow and the second is the distal artery perfused by a lateral branch. The end of flow has a small number of branch vessels. The RCA calcification has a deeper shadow which is just like that of the artery lumen. If the proximal of the RCA CTO is flat or tapered, the wire will pass through the CTO lesion easily. If it is sloped or has many mini vessels, the wire will pass through the CTO lesion less easily and there is a risk that the wire may fail to enter the real lumen.

Recanalization by forward direction

Guiding catheter (GC) technology

The choice of GC is important. Proper GC can give stronger holding power, which will make the wire pass through the lesion easily. Commonly, using AL0.75-1, GL3.5, REBU 3.5-4.0 and SAL 1.0-1.5 catheters can enhance the success rate [Zhang et al. 2010]. A similar sized catheter 7 F can give more holding power than a 6 F [Liu et al. 2011; Capodanno et al. 2010]. Some cases may have an abnormal start located at the left or antetheca of the aortic artery. Others may also show the beginning of stenosis of the RCA. Both these conditions can result in poor GC holding power. One can put a 5F GC into a 6F GC, getting into the RCA via a side hole. This method can give the most holding power, helping the wire/balloon/stent to pass through the CTO lesion [Liu et al. 2011; Muramatsu et al. 2010].

Wire technology

First, a soft wire should be inserted into the RCA until the start of the CTO lesion. Then a mini catheter is pushed along the wire to that point. According to the hardness of the lesion, Pilot 50-200, Mirercle 3.5-12, Conquest, Conquest-pro or Mirercle 8-20/20-40 hard wire is often used [Funatsu et al. 2010]. Because these wires have more penetrating power, the CTO lesion can be pierced easily.

Another technological point is that the wire tip is operated according to the intervener’s judgment. The wire must go forward in the real lumen of the RCA. If the wire passes out of the artery wall it should be kept at that position and not pulled out. Another wire can be inserted into the RCA to proceed [Fang et al. 2009]. In most cases, however, the wire will pass into the real lumen.

In those cases with a sloping arch top, Conquest, Conquest-pro, Mirecle 4.5-12 or Mirecle 8-20/20-40 wire are used [Mamas et al. 2009]. The aim is to have an accurate start and to control the process exactly. In these conditions, wire with hydrophilic coating should not be considered because it gets into the branches easily [Karmpaliotis et al. 2012]. If the wire gets into a branch vessel at the middle of the CTO lesion, another wire should be inserted into the lesion going through CTO lesion or with a mini balloon dilating it [Dykla et al. 2009]. In some cases, the main artery has a little branch vessel. Another soft wire can be inserted into the real lumen of the artery to expand it.

If the wire gets in the interlayer, another wire should be inserted into the real lumen, dilating and stenting. Hydrophilically coated wire, which gets easily into the interlayer artery [Safley et al. 2008], should not be used.

In cases with severe calcification lesion, a soft wire and a mini catheter are first inserted into the tip of the CTO lesion, before changing to a harder wire to rub the lesion. A mini catheter will give additional holding power, making passage through the CTO lesion easier. This method can increase the success ratio [Sheiban et al. 2007].

Balloon technology

Commonly, doctors first use a mini balloon to dilate the CTO lesion and then change to another large balloon to expand it. If the mini balloon cannot go through the CTO lesion, another wire can be inserted into the RCA to increase the holding power and to provide a track. Otherwise, a soft wire and a mini balloon can be inserted into a branch, expanding it to anchor the guiding catheter [Ozawa, 2006]. Another method is to put a stent in the proximal artery and expand it. This can give some extra anchoring power to help the mini balloon pass through the CTO lesion [Kim et al. 2012]. Finally, if all these methods are unsuccessful, three wires can be put through the CTO lesion; one wire is then pulled out and the mini balloon is then passed through the lesion.

Stenting technology

Successful stenting of the RCA is the key to all operating procedures. Commonly, a stent is first put into the distal artery, then stented step-by-step to the proximal artery. But often it is not possible to put a stent into the distal artery. In these cases double wires are used, putting the stent into the stem position and expanding it. Often another stent can then go through it easily into the distal lesion – the first stent having expanded the lumen, the second double wires having anchor power. If this is not possible, the stent escapes and the PCI procedure fails [Claessen et al. 2013].

In some cases stent expansion is poor, in which case a high-pressure balloon can be used, expanding it to 20–24 times atmospheric pressure. If the lesion is too hard to improve by high-pressure balloon and stenosis is <30%, nothing can be done about it [Migliorini et al. 2011].

Recanalization by backward direction

Requirements

The distal artery of RCA CTO is developed by LCA or RCA. A bridge side branch vessel (BSBV) is enough to cover the mini balloon. The BSBV is relative to the straight with no sharp turns. The best way is through the interval branch artery [Taniguch et al. 2011]. The LCA must not have serious stenosis of more than 90%, the ejection fraction must be >45% and there must be no serious valve disease. All important organs should be about normal.

Choice of BSBV

The first step is to choose the interval branch as BSBV to put the soft wire into the distal of the RCA. If the interval branch ruptures, the blood must not go into the pericardial cavity. Another choice is the branch vessel under the pericardium. However, performing the procedure in the latter can lead to the risk of bleeding from the pericardium [Sheiban et al. 2007] and so many doctors prefer the interval branch as the BSBV.

Mini catheter angiography

The LCA branch chosen must undergo selective angiography by mini catheter to observe the BSBV’s condition in at least three positions. This step is critical to successful backward PCI. Only by this it is possible to judge whether the soft wire has passed through the BSBV [Sheiban et al. 2007].

Soft wire technology

‘Run-through’ or ‘field ST’ wire is chosen in many cases because it has perfect passing ability and maneuverability [Ozawa, 2006]. If the wire goes into the middle of the branch, the wire is often pulled out from the micro catheter to show the path of the wire in order to find the real lumen. We then adjust the direction of the wire to the RCA distal. After that the micro catheter can be pushed into that position and a change made to another hard wire to get through the lesion [Morrison, 2005].

Reverse wire technology

After the wire passes through the CTO lesion into the RCA proximal, it should be maneuvered into the right guiding catheter. An extending wire is added and then it is pushed out of the catheter. If the wire does not get into the guiding, a snare can be used to arrest the wire into it [Liu et al. 2011; Mamas et al. 2009]. When all this has been completed, PCI can be performed as above.

Monitoring after PCI

Blood and heart indicators must be monitored as preventing thrombus in stent and heart failure is crucial after PCI [Dykla et al. 2009; Claessen et al. 2013].

Platelet examination

This includes platelet count, adherence–assemble function and gene polymorphism expression [Capodanno et al. 2010; Safely et al. 2008]. If the platelet number is greater than normal, the patient has a thrombus tendency or less than the normal risk of bleeding. When abnormality of adherence–assemble function and gene polymorphism expression are combined, the patient also has a higher thrombus tendency. Two or three kinds of antiplatelet drugs are often combined to prevent thrombus in stents [Taniguchi et al. 2011; Funatsu et al. 2010].

Fibrinogen content

According to the chemical concentration gradient mechanism, the more fibrinogen, the more the thrombus tendency. If the fibrinogen content is >3.4 mmol/l, the activated clotting time (ACT) is <300 and the international normalized ratio (INR) is <0.9, the patient is considered to have a thrombus tendency [Zhang et al. 2010; Kim et al. 2012]. Under this condition some batroxobin is injected to reduce the level of fibrinogen.

Kidney function

Many studies have shown that the abnormalities of kidney function can increase bleeding risk, especially in patients with severe renal insufficiency [Ozawa, 2006; Morrison, 2005]. Heart function can also be reduced. The contrast agent used for PCI also has a damaging effect on renal function; after PCI, many patients have lowered renal function [Ozawa, 2006]. For the patient with renal insufficiency, doctors should give a renal protective agent and increased contractility drugs.

ECG and blood pressure (BP)

Because the myocardium has sustained reperfusion injury, many patients suffer from arrhythmia and BP fluctuation [Stiermaier et al. 2013; Muramatsu et al. 2010; Ozawa, 2006]. For stable recovery of the patient, intensive observation is important. If the patient has heart failure, arrhythmia and BP fluctuation should be positively treated, making use of antiarrhythmic and vasopressor agents, according to the patient’s condition.

Cardiac ultrasonography

The aim of cardiac ultrasonography is to detect pericardium, myocardium beating width and ejection fraction. It helps to identify the basic condition of the heart and prevents the occurrence of some malignancy events.

X-ray

X-ray examination can help to show the condition of the lung and indirectly judge heart function. This is especially the case when the patient has a fever. Some patients may have flocculent shadow and it must be established if it is infective or due to edema.

Intensive treatment after PCI

The treatment given after PCI is vital. It also relates to the long-term prognosis.

Antiplatelet drugs

These are essential to the patient undergoing PCI. Many doctors consider that as long as the patient takes aspirin and clopidogrel they will be safe. In practice, this is a mistaken idea: about 20–30% patients have partial or complete tolerance to aspirin and clopidogrel [Capodanno et al. 2010; Mamas et al. 2009; Ozawa, 2006]. Thrombus is common during stenting in these patients. The main reason for this tolerance is polymorphism in platelet genes. Alternative drugs such as prasugrel, rivaroxaban or tirofiban should be substituted. Antiplatelet drugs should be taken for at least 8 months.

Anticoagulant drugs

Low molecular weight heparin is injected subcutaneously for at least 5 days. If the patient has bifurcation lesion/long lesion or more than three stents implanted, this anticoagulant period should be prolonged [Muramatsu et al. 2010; Ozawa, 2006]. After that if the patient still has a hypercoagulability tendency, warfarin should be administered for >1 month. While taking oral anticoagulant drugs, an INR ratio maintained at 1.5–2.0 is commonly expected. If the thrombus is located in a ventricle, administration of the oral anticoagulant drug should be prolonged.

Statins

Statins must be taken after PCI because they can stabilize and ease the stenosis lesion of coronary artery. Many studies have proven that statins can decrease major adverse cardiovascular events [Brady et al. 2013; Capodanno et al. 2010; Karmpaliotis et al. 2012]. Treatment of the small coronary artery depends completely on statins and a K passageway opening agent (nicorandil) [Dykla et al. 2009; Morrison, 2005].

Angiotensin-converting enzyme inhibitors (ACEIs)/angiotensin II receptor blockers (ARBs)

ACEIs and ARBs can not only lower the peripheral resistance and BP, they can also improve the effect on myocardial remodeling. During PCI these therapeutic agents can prolong the prognosis and reduce major adverse cardiovascular events [Ozawa, 2006; Claessen et al. 2013]. All these depend mainly on the lifting of heart function.

β-blockers

β-blockers can depress sympathetic nerve action, decrease the quantity of oxygen consumption, improve myocardium remodeling and enhance the heart function. Many studies have proven that β-blockers can markedly prolong the prognosis of the patient with heart failure. Almost all guidelines worldwide stress the importance of β-blockers in lowering major adverse cardiac events.

Nitrate drugs

These can decrease the front and back load of the heart, expand the coronary artery and increase blood flow volume. They are often used to treat coronary arterial disease, but long-term prognosis is not improved.

Improving energy metabolism

Normally, myocardium cell metabolism involves ~65% β-aliphatic acid oxidation and ~35% glucose oxidation. β-Aliphatic acid oxidation is heightened and glucose oxidation is suppressed in hypoxia [Safley et al. 2008; Ozawa, 2006]. Under this condition, the energy generated is less than normal. Trimetazidine can increase the glucose oxidation ratio, which may enhance more adenosine triphosphate (ATP) energy and depress β-aliphatic acid oxidation.

Sports medicine

Many clinical studies of ‘lifestyle medicine’ have proved that walking and appropriate exercise can improve the body’s condition and heart function [Zhang et al. 2010; Muramatsu et al. 2010; Safely et al. 2008], enhance life quality and prolong lifespan. The degree of sport must be added step-by-step and rely on personal capability. If the patient exercises too much or too fast, it can be harmful to heart function and induce acute left heart failure or even death.